A peck drill is a commonly used for drilling holes in products being manufactured. The peck drill has a pneumatic motor that rotates a drill bit. A pneumatic piston advances the drill bit as it is rotated. A hydraulic damper controls the speed at which the piston moves the drill bit forward.
The hydraulic damper has a cylinder and a piston with a rod extending from it, typically in a rearward direction. The pneumatic piston also has a rod that extends from it, normally in a rearward direction. A cross member is mounted to the end of the pneumatic piston rod for movement therewith. A pneumatically actuated retainer member is mounted to the end of the damper rod for movement therewith. The retainer device has a releasable lock that will allow the retainer device and the damper rod to move forward but prevent it from moving rearward unless the total depth of the hole has been reached. The cross member mounted to the piston rod contacts the retainer member and pushes it and the damper rod forward. The speed of the forward movement is restricted by the hydraulic cylinder of the damper assembly.
Being a peck drill, a controller repeatedly retracts the piston rod and the drill bit every few seconds. When the piston rod retracts, the damper rod does not retract because of the retainer device. Consequently, when air pressure is again supplied to the piston, it will advance only until the cross member arm contacts the retainer device. When the total depth is reached, the control unit causes the retainer device to release, enabling the damper rod to move to the fully retracted initial position.
One problem that may occur is that the retainer device will sometimes not release the rod when the total depth has been reached. The piston would still retract normally. The operator would then push the start button to drill a new hole, not realizing that the damper rod is still in the forward position because the damper rod is typically enclosed by a housing. If the operator pushes the start button when the damper rod is still in the forward position, the piston will drive the drill bit forward at an uncontrolled, rapid speed that can damage the work piece.